Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationCondensation polymerisation, and making a polymerDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Predicting and Identifying Reactions
Groups 1, 7 and 0, and why they behave as they do
- 3 things to know
- Paper 4
Overview
The physical properties of the Group 1 metals and their reaction with water, the states, colours and diatomic molecules of chlorine, bromine and iodine, why the noble gases are unreactive and their properties, the outer electrons and ions of Groups 1 and 7, why reactivity rises down Group 1 and falls down Group 7, predictions for rubidium and astatine, halogen displacement, and noble gas boiling points.
What you need to know
Answer each one before you reveal it.
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Key term
What are the physical states of chlorine, bromine and iodine at room temperature?
Key term
What colours are chlorine, bromine and iodine?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What are the main physical properties of the metals in Group 1?
Model answer
They are soft enough to cut with a knife, have low densities and low melting points, and are shiny when freshly cut but tarnish quickly in air.
- 2
What two products are formed when a Group 1 metal reacts with water?
Model answer
A metal hydroxide, which dissolves to give an alkaline solution, and hydrogen gas.
- 3
Describe what is observed when a small piece of sodium is dropped onto water.
Model answer
It floats, melts into a ball and fizzes as it moves rapidly across the surface, leaving an alkaline solution behind.
- 4
What are the physical states of chlorine, bromine and iodine at room temperature?
Model answer
Chlorine is a gas, bromine is a liquid and iodine is a solid.
- 5
What colours are chlorine, bromine and iodine?
Model answer
Chlorine is pale green, bromine is red-brown and iodine is a dark grey solid that forms a purple vapour when warmed.
- 6
In what form do the elements of Group 7 exist?
Model answer
As diatomic molecules of two atoms sharing a pair of electrons, such as Cl₂ and Br₂.
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